Research in the pathophysiology and epidemiology of asthma has guided development of treatments that are effective in management of symptoms and improving pulmonary function in children. However, there are many significant questions that remain to be addressed about asthma management. This proposal will address two of these important issues. In the first propose a 3-year randomized, double-blind trial comparing the effects of four treatments on chronic airway obstruction in children with asthma 5-15 years of age: 1) high dose inhaled steroid (IS) + leukotriene receptor antagonist (LA), 2) high dose IS alone, 3) low dose IS + LA, and 4) low dose IS alone. Chronic airway obstruction is defined as an abnormal FEV1/FVC after maximal bronchodilation on 2 occasions separated by 6-8 weeks. Primary hypothesis: Compared to low dose IS alone, high dose IS + LA will improve post bronchodilator FEV1 and FEV1/FVC over three years of study, taking into consideration age, gender, race, duration of asthma on entry into the trial, initial FEV1, and initial FEV1/FVC. Effects of high dose IS alone and low dose IS + LA will be intermediate. In the second, we propose a nine month randomized, double-blind, placebo-controlled prospective trial comparing three therapeutic approaches to young children (1-3 years of age) with mild intermittent asthma and recurrent viral respiratory infection-induced wheezing episodes: 1) inhaled bronchodilators at inception of a URI syndrome, 2) inhaled bronchodilators and high dose nebulized inhaled steroid (IS) at inception of a URI syndrome, and 3) ongoing low dose IS with inhaled bronchodilators and high dose nebulized IS at inception of a URI syndrome. For each of the groups, if symptoms progress, as defined by development of wheezing and/or cough unresponsive to inhaled bronchodilators, oral systemic steroids will be added. Primary hypothesis: Compared with the conventional therapy consisting of the sequential addition of systemic corticosteroids to inhaled bronchodilators (Group 1), early intervention with IS at the onset of symptoms suggestive of a URI will decrease the total number of days with wheezing over a 7 month period. The administration of high dose IS at the onset of URI symptoms (Group 2) will be at least as efficacious as the administration of low dose IS as maintenance therapy with high dose IS added at first sign of URI symptoms (Group 3).